Modern screen-based display devices are typically flat-screen monitors such as liquid crystal display (LCD) or plasma screen displays. Such devices can be mounted on elevated support devices such as a support arm which can then be secured to a surface such that the flat-screen monitor is held above or in front of the surface.
Support systems for monitors are known which allow for movement in three dimensions of the head, mount or bracket on which the monitor is mounted. This is so as to allow for a full range of adjustment of the monitor. GB 2 438 581 and U.S. Pat. No. 7,438,269 both disclose mounts or brackets including an arcuate connection which allows a monitor to be pivoted about a substantially horizontal virtual pivot axis. In U.S. Pat. No. 7,438,269, the virtual pivot axis passes through the centre of gravity of a monitor or display so as to reduce the forces necessary to hold the mount in place at a selected position on the arcuate connection.
In order to allow for adjustment about a substantially vertical axis (or an axis orthogonal to the axis of the arcuate connection), known arrangements such as those disclosed in GB 2 438 581 and U.S. Pat. No. 7,438,269 have a second pivoting mechanism entirely separate from the first. The second pivot is a separate vertical rod-like element defining a vertical axis. This second pivot is distinct and separated from the pivot of the arcuate connector.
These prior art arrangements require two separate and distinct pivot arrangements. They are therefore relatively complicated and expensive to build, have two pivots (and therefore more moving parts) which can fail and are relatively unsightly.
Support systems for monitors comprising an articulated arm arrangement for raising and lowering a monitor are known with tiltable mount or bracket mechanisms which keep the monitor in the same plane as the arm moves up and down. The known arrangements such as those disclosed in US 2004/0245419 have a four bar linkage or parallelogram arrangement in which there is a second link or arm below (or above) and parallel to the main support arm and pivotally coupled to the tiltable mount or bracket on which a monitor is mounted. The second link or arm is pivotally coupled to the mount or bracket below (or above) the pivot between the main support arm and the mount, and also pivotally coupled to the base or support element to which the other end of the main support arm is pivotally coupled at a point below (or above) the pivot between the main support arm and the base or support element. The main support arm and the second link arm are parallel to each other and the linkage (which can be considered to be a line drawn between) the pairs of pivots on each of the base element and mount are also parallel to each other.
This parallelogram four-bar linkage means that as the support arm is moved up and down the linkage between the two pivots on the tilt mount remains in the same plane parallel to the linkage between the two pivots on the base element.
A disadvantage of the known four-bar parallelogram linkage arrangements is the need to provide a second link parallel to and separate from the support arm. Such arrangements therefore must have a second visible (and therefore unsightly) link or arm parallel to the main support arm. Alternatively, such parallelogram arrangements have a large deep casing which can house the main support arm, the second parallel link and the space therebetween. This is bulky and therefore also unsightly.
Another problem with articulated support arms for loads such as monitors or display devices which move up and down as they pivot about a horizontal axis, is the varying torque created by the constant weight of the monitor applied about the horizontal axis. As the arm moves up and down the distance from the load at the end of the support arm to the other end of the support arm and the pivot between the support arm and its base varies.
In order to oppose this varying torque it is known (see, for example, US 2004/0245419) to provide a compression spring which provides a variable force to create a torque to oppose and match the torque created by the weight of the load. The spring is subject to a cam arrangement which controls the degree of compression of the spring and hence the force it applies. Cam arrangements of the type disclosed in US 2004/0245419 are relatively complex and hence expensive to make.
Another problem with arrangements in which a biased mechanical spring, gas spring or other biasing element provides the force necessary to balance the weight of the monitor is the need to set up or adjust the spring or biasing element when a monitor is placed on it so that the torque provided by the spring closely hatches the torque provided by the weight of the monitor. This is done by a manual adjustment of the spring position of a surface against which the spring rests for a compression or expansion spring, and for a gas spring (which provides a constant force) by adjustment of the orientation and position of the end of the gas spring relative to the monitor mount, monitor and principal longitudinal axis of the support arm (i.e. the geometry of the lines of application of the various forces/torques is adjusted to achieve balance).
The installation technician manually adjusts the position of an end of the spring using trial and error until the torque provided by the weight of the monitor is balanced by the torque from the spring and the monitor can be moved easily and yet remains in position when positioned at a particular elevation by an operator. The process of such manual installation is particularly cumbersome and time consuming when a large number of monitors and support arms are being installed as is often the case when, for example, an office is being fitted out with a number of identical monitors and support arms.